A conventional integrated ferroelectric capacitor includes one or more ferroelectric layers sandwiched between a bottom electrode and a top electrode. The ferroelectric layer(s) may include, for example, PZT, SBT or BLT. The capacitor is covered with one or more interlayer dielectric layers, normally Tetraethyl Orthosilicate (TEOS), and connection to the top electrode is achieved by etching a window through the interlayer dielectric layer(s) and filling the window with a metal filler. The bottom electrode is mounted on a substrate, the electrical connection to the bottom electrode being via a metal plug through the substrate. To make the connection between the bottom electrode and the plug, a window is formed through the interlayer dielectric layer(s), through the other layers of the capacitor and into the plug. A liner is formed in this window and a metal filler is deposited in the bottom of the window to make the contact between the bottom electrode and the plug. The liner and the metal filler are etched to leave just the contact to the plug. Encapsulation layers and cover layers are added to protect the resultant capacitor.
Conventional integrated ferroelectric Random Access Memories (FeRAMs) including one or more of the above types of capacitors generally suffer from a number of problems. These problems are predominantly due to hydrogen damage generated during the backend process of application of the intermetal dielectric layer and deposition of the encapsulation and/or cover layers. Processes such as plasma-Tetraethyl Orthosilicate (p-TEOS) deposition which is used to apply the one or more interlayer dielectric layers to the capacitor, RIE (reactive ion etch), and sintering are known to damage the capacitor due to the reducing effects of the hydrogen released. Furthermore, processes such as plasma-enhanced chemical vapour deposition (PECVD) which uses SiH4-based gas chemistry, generate hydrogen ions and electrons which can diffuse into the ferroelectric layer of the capacitor and then pin ferroelectric domains. The hydrogen ions and electrons may also cause decomposition of the ferroelectric layer as well as decomposition of electrode materials, such as SRO. These types of effects can lead to serious degradation of the ferroelectric performance of the capacitor. The damaged capacitors have more defects resulting in more space charge formation and their ferroelectric properties degrade.
Conventional attempts to reduce the hydrogen diffusion in capacitors include the deposition of several layers of encapsulant and cover layers over the capacitor, usually by a sputtering process or atomic layer deposition (ALD). These layers are typically formed of Al2O3, but it is also known to use other oxides such as TiOx. Such conventional techniques have limited success as the encapsulant and cover layers are insufficient to prevent hydrogen diffusion.
Other attempts have been made to reduce the effect of hydrogen on the capacitor, for example, by burying or recessing the bottom electrode in the substrate, however, these have not been found to be effective in preventing hydrogen damage.
In view of the foregoing problems with conventional processes and devices, a need exists for a method for inhibiting hydrogen damage during the manufacture of a capacitor.